code: def test_spec_hierarchy_from_list():
      hierachy_cols = ["col1", "col2"]
      hierarchy_spec = spec_hierarchy_from_list(hierachy_cols)
  
      assert len(hierarchy_spec) == 3
      assert hierarchy_spec[0] == ["Total"]
      assert hierarchy_spec[1] == ["Total", "col1"]
      assert hierarchy_spec[2] == ["Total", "col1", "col2"]
  
file_path: mindsdb/tests/unit/ml_handlers/test_time_series_utils.py
imports: import pandas
  from statsforecast.utils import AirPassengersDF
  from mindsdb.integrations.utilities.time_series_utils import transform_to_nixtla_df, get_results_from_nixtla_df, infer_frequency, get_best_model_from_results_df, spec_hierarchy_from_list, get_hierarchy_from_df, reconcile_forecasts
label_desc: Use image node_id 5 for calling a global function with example usage: test_spec_hierarchy_from_list() without return types